The present invention related to a frictional material, in particular, to the frictional material comprising carbon fiber/carbon composite infiltrated with metal and provides a frictional material for brake wherein the friction characteristic, wear resistance and mechanical strength are improved and still friction coefficient of moderate to high order can be obtained.
The carbon fiber/carbon material (hereinafter abbreviated as C/C composite) is an industrial material obtainable in such a way that the thermally molded article used carbon fibers (polyacrylonitrile type, pitch type, etc.) as reinforcement materials and pitch, phenol resin, furan resin, etc. as binders is carbonized or graphitized by firing. When using as the frictional material for brake etc., said C/C composite is excellent in the heat resistance, but, with a combination of the frictional material comprising C/C composite with the opposite member for friction, there is a limit to satisfy the friction performances diversifying depending on the needs. Moreover, when using as the opposite member for friction, there has been a shortcoming that the mechanical strength is insufficient.
The invention has been made to dissolve such shortcomings accompanied with C/C composite and the friction performance has been improved drastically by infiltrating small amount of metal into pores of C/C composite to achieve the anticipated object.
The metal-containing composite materials allowed the metal to be contained in C/C composite are known publicly. For example, in Japanese Patent Publication No. sho 53-27205, a composite material excellent in the strength and lubrication performance is obtained by allowing nonferrous metal or alloy consisting of two or more thereof with a melting point of 200.degree. to 1100.degree. C. to be contained in C/C composite with a porosity of 10 to 50 vol. % (content of carbon fibers : 40-60 vol. %) in amounts of 10 to 50 vol. %. Moreover, also in Japanese Unexamined Patent Publication No. sho 60-162748, a composite material buried the communicating pores in the carbon matrix of C/C composite with metal is proposed. In the latter, there are no distinct descriptions about the porosity and the content of metal (in the example, only the amount of carbon fibers is described to be about 70 vol. %), but, since the material is high in the strength at normal temperature and excellent in the heat resistance, aero and space use and uses as brake shoes and other constitutional materials for motor car and airplane are suggested.
Two inventions aforementioned are entirely different from the present invention in the objects and the friction performances thereof. In particular, the invention shown in Japanese Patent Publication No. sho 53-27205 relates to a sliding material, the use of which differs from the frictional materials for brake etc. contemplated in the present invention.
As a result of extensive investigations on the friction performance of C/C composite described above infiltrated with metal, the inventor has found that remarkable improvement of performance can be obtained within a fixed range of infiltration lower than the amount of infiltrated metal described in Japanese Patent Publication No. sho 53-27205.